1. Field of the Invention
The present invention relates to an image forming apparatus such as, for example, a copier or a printer that is provided with a function of forming an image on a recording medium such as a sheet.
2. Description of the Related Art
Up to now, an image forming apparatus using an electrophotographic system is constituted by a photosensitive member serving as an image bearing member, a charge apparatus, an exposure apparatus, a developing apparatus, a transfer apparatus, a cleaning apparatus, a fixing apparatus, and the like. An image is formed on a recording medium by performing the following procedures (electrophotographic process).
First, the photosensitive member is uniformly charged (charging procedure), a latent image is formed on the photosensitive member that has been subjected to the charging processing (exposure procedure). Then, the latent image formed on the photosensitive member is developed by toner serving as a developer (developing procedure), and this toner image is transferred from the photosensitive member to the recording medium (transfer material) (transfer procedure), so that the toner transferred to the recording medium is fixed on the recording medium (fixing procedure). The residual toner after the transfer is removed and cleaned from the photosensitive member (cleaning procedure).
The residual toner on the photosensitive member after the transfer procedure is removed from a photosensitive member surface by the cleaning apparatus and remains in the cleaning apparatus to become waste toner. However, from the viewpoints of environmental protection, effective utilization of resources, miniaturization of the apparatus, and the like, no waste toner is preferably produced. In view of the above, Japanese Patent Laid-Open No. 59-133573 or the like discloses a cleaner-less system image forming apparatus in which the residual transfer toner is collected in the developing apparatus (so-called “cleaning simultaneous with developing”), and the residual transfer toner is removed from the photosensitive member to be collected and reused.
However, in the image forming apparatus adopting the cleaner-less system, the charging processing is performed by the charge apparatus in a state in which the residual toner after the transfer is adhered onto the photosensitive member. When the photosensitive member is charged by the charge apparatus in a state in which this residual toner is present, the charging is conducted on both the residual toner and the photosensitive member. In the above-described charging on the photosensitive member from above the toner, in a part where the residual toner is present, a charging potential on the photosensitive member is disturbed by the toner as compared with a charging potential (Vd) at the photosensitive member in a normal case where the toner is absent. Thus, the potential on the photosensitive member is decreased as compared with the charging potential (Vd) in a part where the residual toner is absent. Since the charging on the photosensitive member is disturbed in proportion to the amount of the residual toner, when the amount of the residual toner is high, the decrease amount of the photosensitive member charging potential is increased. Therefore, when the cleaning simultaneous with developing is performed in a state in which when the amount of the residual toner is high to some degree, the residual toner itself is collected by the developing apparatus, but the charging potential on the photosensitive member in the relevant part is low. If a latent image is formed by exposure in a state in which the charging potential on the photosensitive member in the part where the residual toner exists as described above is low, a latent image potential is decreased (an absolute value of the potential is decreased) in the relevant part. Thus, a density in a half-tone image in particular is thickened, and a so-called positive ghost may be generated.
As measures for this problem, Japanese Patent Laid-Open No. 1-50089, for example, discloses an image forming apparatus in which a member for uniformly dispersing the residual toner is provided on an upstream side of the charging member. In this apparatus, the residual toner is sucked and removed from the photosensitive member by a memory removal member before the charging procedure after the transfer procedure. In this manner, since the residual toner is collected and removed from the photosensitive member, it is possible to suppress the decrease in the charging potential caused by the toner, and the generation of the positive ghost caused by the residual transfer toner is suppressed.
However, a problem occurs that the above-described memory removal member is disadvantage in the cleaner-less system when a space and a cost are taken into account.
This is because, although the miniaturization of the apparatus is to be advanced from the viewpoint of the space, if the miniaturization is advanced, the photosensitive member, the charge apparatus, the exposure apparatus, the developing apparatus, and the transfer apparatus are close to each other, and it is difficult to secure the space for the memory removal member to be arranged between the transfer apparatus and the charge apparatus. In addition to this, since the memory removal member is provided, the cost for the member is generated.